How do I gain his trust?

When I first met my current boyfriend, there was a little conflict because he and another guy both liked me, and they were friends. I was upset because I didn’t want to come between friends and I wanted a guys opinion so I went to one of my guy friends. He took advantage of the situation and tried to get with me while I was vulnerable. after that, I chose to be with my boyfriend but I was having trouble telling him about what had happened because I knew he needed to know. he was out of state and I was waiting to talk to him in person. well one of his friends decides to spread a rumor that I had sex with someone and my boyfriend confronted me. I ended up telling him about what happened when I went to talk to my guy friend. he was very hurt because he felt cheated on. but, a week later, he told me he wanted to stay with me. this was last feb. now fast forward to this october. I was talking to a guy friend and my boyfriend didn’t want me to. I told him I agreed but I was having trouble telling this guy, “I can’t talk to you because my boyfriend thinks we’re flirting” I was trying to stop talking to him slowly and apparently my boyfriend went into my a social site account and saw that I still had a conversation up with him. he didn’t seem too upset but I think it made him think about the first thing that happened. now I have been trying very hard to show my boyfriend I love him. and I want to be with him. and he has been all lovey dovey but the other night he brought up these things again, along with how he thought that in the last month we werent talking enough. I hate that he doesn’t share his feelings because if he had just told me that, he would know it’s because I’ve had somepersonal issues as of late. now he is “thinking” about what happened at the beginning of our relationship and is worried that I don’t trust him. atleast, thats how I’m interpreting what he was saying. How do I gain his trust? I think its been brewing in him because he doesn’t share hows he is feeling because he doesn’t want to hurt me. when we fought, I told him I loved him, told him im sorry but I can’t change what was done, and I can only promise to be as good to him as I can and to share and to be open with him in the future. I know this is long, if you read it, thank you! lol I’m just looking for what I can say to him because he has been “thinking” for 3 days and it kills me not to be talking…I hate this…